The present invention relates in general to data transmission between the switching systems of a telecommunication network and more particularly to a remote data link controller for formatting, transmitting and receiving control data between the peripheral processors of a plurality of switching systems.
In modern digital telecommunication switching systems a concept of network modularity has been designed allowing the interconnection of small switching systems remote to a larger host system. These remote switching systems have capacities to handle between a few hundred and a few thousand telephone subscribers. The remote switching systems are normally used in areas where the installation of a large switching system would be uneconomical.
A high speed digital data link typically interfaces the host switching system to the remote system through which large amounts of voice and control data are exchanged. The voice data normally comprises subscriber calls switched through either the host or the remote system. The control data may be status exchanges between the host and the remote, i.e. centralized administration, billing and maintenance, or the direct control of the operation of the remote by the host.
The control data exchanges are originated in the sending system peripheral processor transmitted over the high speed digital data link to the receiving system peripheral processor where the data is interpreted. In order to relieve each peripheral processor from the burden of controlling the data link a remote data link controller is implemented in each system which performs all tasks involved in the formatting, transmission and reception of the control data.
The remote data link controllers are connected to each other via digital spans. These digital spans may be T1, T2 or T1C, T3 carriers using DS1, DS2 or DS1C, DS3 data formats, respectively. These digital spans transmit data at high speeds serially at a rate of approximately 1.5-45 megabits per second.
One method presently used in the industry for controlling a data link is the serial data link controller (SDLC) protocol developed by IBM INCORPORATED. The SDLC protocol requires the SDLC circuitry to handle one link on a dedicated basis. That is, in a system where the host connects to for instance, 16 remote units, a single SDLC circuit would be required for each link. Because of the complexity of the SDLC circuitry it is impractical to control all 16 data links with a single SDLC circuit.
Accordingly, it is the object of the present invention to provide a single remote data link controller which can be shared among a plurality of data links for formatting, transmitting and receiving control data between the peripheral processors of a host and a plurality of remote switching systems.